Catalytic converters are used to reduce undesirable emissions in the exhaust gases of internal combustion vehicle engines and are located in exhaust systems connected to the engines. A catalytic conversion process operates most efficiently within a specific temperature range, and it is relatively inefficient when operating at a temperature below 800.degree. F. (425.degree. C.). Since a catalytic converter is relatively cool when an engine is initially started, it takes some time for the exhaust gases to heat the converter to its efficient operating temperature.
Light-off converters have been developed to minimize start-up emissions. Light-off converters are smaller and mounted in close proximity to the exhaust ports of the engine so that they heat quickly, due to their small size and proximity to the engine exhaust ports. A larger converter or underbody converter, is also used in conjunction with the light-off converter.
One problem is that catalytic converter elements may begin to breakdown at high temperatures; for example, catalytic converters can be damaged at temperatures not much above 1350.degree. F. (735.degree. C.). This problem is most pronounced in light-off catalytic converters due to their small size and close proximity to engine exhaust ports where temperatures may exceed 1400.degree. F. (760.degree. C.).
The problem addressed by this invention is that of providing bypassed a catalytic converter system that provides effect catalytic operation shortly after engine start-up and long term light-off catalytic converter durability by controlling the temperature of the catalyst in the light-off catalytic converter.
These and other objects and advantages are achieved by the invention as summarized below.